In the letter, he said his family announced its "complete renunciation" of Mosab Yousef. The father said he was sorry to take such a step but said he had no choice after his son "disbelieved in God...and collaborated with our enemies," he said.

The elder Yousef, who helped found the militant Islamic group two decades ago, was humiliated last year when his eldest son announced he had converted to Christianity. Then the son told an Israeli newspaper last week that he had helped Israeli intelligence foil militant attacks and hunt down Hamas leaders — including his father.

As the Gaza conflict rages on, Yousef appeared last this week on CNN with Don Lemon where he said, “Hamas doesn’t care about the lives of Palestinians. Does not care about the lives of Israelis or Americans. They don’t care about their own lives. They consider dying for the sake of their ideology a way of worship. And how can you continue in that society?”

Lemon asked if peaceful co-existence was possible with someone who wishes to see you destroyed.

Yousef was blunt:

Well, Hamas is not seeking co-existence and compromise. Hamas is seeking conquest and taking over. And, by the way, Israel – the destruction of the state of Israel is not Hamas’ final destination. Hamas’ final destination is building the Islamic Caliphate, which means an Islamic state on the rubble of every other civilization. These are the ultimate goals of the movement.